Soft contact lenses that are hydrophilic and form hydrogels when hydrated (hereinafter referred to as hydrogel lenses) are typically sold already hydrated for several reasons. Lenses already hydrated and, therefore, packaged in solution can be immediately worn upon purchase, by merely removing the lens from the package, without any subsequent treatment of the lens or additional preparation by the consumer. Lenses have already acquired their desired shape for use in the hydrated form and can, therefore, comfortably fit on a patient's eyes. In contrast, a hydrogel contact lens, in the dry state, cannot be safely or comfortably placed on the eye and must first be hydrated prior to being worn by the customer.
While consumers may enjoy the convenience of ready-to-wear lenses directly out of their package, several disadvantages and costs are associated with such hydrated lenses. It can be recognized that a large percentage of total lens cost is attributable to the cost of hydrating, packaging, and sterilizing such lenses. Lenses have traditionally been wet packaged in vials or, more commonly, blister packs. In either case, the addition of hydrating solution adds to the overall weight and volume of the finished product and increases shipping and storage costs. When blister packs are used, they are sealed with lid stock made of plastic and aluminum to prevent the hydrating solution from escaping. The use of lid stock further increases the cost of packaging hydrated lenses.
Another disadvantage of manufacturing and packaging a hydrated lens is that the hydrating solution not only complicates the packaging, but creates an environment that is potentially susceptible to bacterial growth. Furthermore, the hydration and sterilization of the lenses can make them more susceptible to hydrolysis or degradation. (The shelf life of a particular lens can vary depending upon its composition, porosity, rigidity, thickness, etc.) Also, the saline solution used in packaging contains salt that is aggressive towards lid-stock packaging and can, therefore limit the shelf life not only of the lens itself but the blister packs used to contain them. Of course, the integrity of the package cannot be compromised without jeopardizing the sterility of the hydrated lens. Thus, the risk of package degradation and bacterial growth can limit the shelf life of hydrated lenses.
The vulnerability of hydrated lenses and/or their package to gradual degradation, with consequent bacterial growth on the lens, thus makes it necessary for manufacturers to include an expiration date with each pair of contact lenses. Typically, the shelf life for wet-packaged contact lenses ranges from two to five years, often only a couple years, commencing from the time the lenses are autoclaved.
Lenses hydrated and packaged in solution must be sterilized. Sterilization of the hydrated lens during manufacturing and packaging is typically accomplished by autoclaving. The autoclaving process involves heating the lens to a temperature of about 121.degree. C. for approximately 20 minutes under pressure. As mentioned above, such treatment may adversely affect the shelf life of the lens. By exposing lenses to high temperatures during autoclaving, polymeric bonds can be weakened or hydrolyzed, accelerating polymer degradation. Furthermore, autoclaving adds additional time and cost to the manufacturing process. Each batch of sterilized lenses may be quarantined while the effectiveness of the sterilization process is tested and confirmed. Also, autoclaving, associated with the packaging of hydrated lenses, has the disadvantage that it can potentially increase lens extractables from the lens or adversely affect the surface treatments or coatings existing on some kinds of lenses.
Even after the manufacture of the lens is complete, the hydration of hydrogel lenses incurs associated costs. Additional volume is needed for maintaining the lens in hydrated form, which can significantly add to the cost of storing, inventorying, and distributing the lenses to the retailer or customer. Furthermore, the above-mentioned limited shelf life associated with hydrated lenses can also add to the cost of storing, inventorying, and distributing the lens, not to mention the increased likelihood that the customer may need to discard expired lenses before they are worn. The limited shelf life of hydrated lenses adds to the difficulty of inventorying such lenses because manufacturers must anticipate the demand for each type of lens and then compare the demand with the existing supply. In doing so, they must also consider the remaining shelf life of stored lenses. Doctors face similar difficulties when purchasing lenses to meet their patients' needs. Unfortunately, consumer demand cannot be determined with certainty. Therefore, the anticipated demand can exceed the actual demand and can result in significant obsolescence costs.
Packaging systems and dispensing systems according to Applicants' invention offer manufacturers a simplified, more cost-effective way to manufacture, store, inventory, and distribute hydrogel contact lenses.